Technical Field
The present disclosure relates to a direct current circuit breaker and more particularly, to a direct current circuit breaker which is capable of shortening a cut-off operation time and reducing a magnitude of a required reverse current.
Description of the Related Art
In general, a direct current circuit breaker is a device used to cut off a system quickly and efficiently for repair and replacement of a device on a HVDC (High Voltage Direct Current) transmission line or distribution line and protection of a device or system at the time of occurrence of a fault current.
FIG. 1 shows a conventional direct current circuit breaker (e.g., see WO2013/045238 A1 (PCT/EP2012/067276)). Referring to FIG. 1, a conventional direct current circuit breaker 100 includes a main electric conducting part consisting of mechanical breakers 110 and 120 and a diode 124 which are responsible for electric conduction of a rated current, a resistor 150, an inductor 160, a capacitor 170 and a surge arrestor 180. In addition, the conventional direct current circuit breaker 100 further includes a pulse generator (PG) 185 which consists of a thyristor 190 and a diode 195 and produces a reverse current for arc extinguishment at the time of current cut-off and a part which consists of a diode 130 and a surge arrestor 140 and absorbs and cancels energy remaining in a line.
An operation of the conventional direct current circuit breaker 100 is as follows. At the time of conduction of the rated current, the mechanical breaker 120 is closed to flow the rated current. At this time, due to a potential difference between a fourth node 104 and a second node 102, the capacitor 170 is charged through a path of the diode 195 of the PG 185→the resistor 150→the capacitor 170. When the capacitor is fully charged, the potential difference between the fourth node 104 and the second node 102 disappears and a flow of current into the PG 185 is cut off. Thus, the direct current circuit breaker 100 is completed to be ready to operate.
When a fault current occurs and the direct current breaker 100 begins to perform its cut-off operation, the mechanical breakers 110 and 120 are first opened. However, the mechanical breakers 110 and 120 are in a state where the fault current continues to flow due to an arc current. Thereafter, the thyristor 190 of the PG 185 is turned on to reversely charge the capacitor 170 through a path of the capacitor 170→the inductor 160→the thyristor 190. When the amount of reverse charging of the capacitor 170 reaches a discharging voltage of the surge arrestor 140, the surge arrestor 140 is brought into an electrical conduction state. Then, the capacitor 170 begins to be discharged and, accordingly, a reverse current flows into the mechanical breaker 120 through a path of the capacitor 170→the surge arrestor 140→the diode 130→the mechanical breaker 120→the diode 195→the resistor 150. Accordingly, the fault current flowing into the mechanical breaker 120 meets the reverse current, thereby producing a current zero point. As a result, an arc of the mechanical breaker 120 is extinguished. A reverse current remaining after the arc extinguishment flows through the diode 125. In addition, energy remaining in a line after completion of the cut-off of the mechanical breaker 120 is absorbed through the surge arrestors 140 and 180 and the capacitor 170 of the PG 185 is recharged to prepare for a next cut-off operation.
However, in the above-described conventional direct current circuit breaker 100, the capacitor 170 of the PG 185 has to be reversely charged in order to create the reverse current at the time of the cut-off operation. Such a process may result in a delay of the cut-off operation. Further, since the fault current increases fast, a larger fault current increased as much as delayed time has to be cut off. This may impose a big burden on the capacitor 170, the mechanical breaker 120 and the surge arrestor 140, requiring parts including a higher capacity, which may result in increase in production costs of direct current circuit breakers.